Air springs of the above type are known and are particularly commonly used in utility vehicles. The rolling-lobe flexible member of the air spring is made of an elastomeric material, preferably rubber or a rubber-like plastic, and has fastening beads at the ends. These fastening beads permit mounting onto the attachment parts such as flange plates or roll-off pistons. The cores of the fastening beads are conventionally made of steel wires.
It is known for the attachment parts such as roll-off pistons and/or covers or attachment plates to be produced from steel, aluminum or glass-fiber-reinforced plastic.
The use of plastic for the attachment parts has the advantage that corrosion is avoided and cost and weight advantages are attained with respect to the use of steel parts. It has, however, disadvantageously been found that the attachment parts made of plastic and the fastening beads expand to different extents at very high and very low operating temperatures of the air spring, and the air spring thus develops leaks because the steel wires as reinforcement cores of the fastening beads and the plastic attachment parts exhibit different expansion behavior.
United States patent application publication 2011/0266728 A1 is incorporated herein by reference and shows the fastening beads of a rolling-lobe flexible member with an embedded bead core made of plastic which is produced in an injection-molding process. The fastening bead of one rolling-lobe flexible member end is of conical form and bears against the associated conical seat surface of the roll-off piston under the action of the internal pressure of the rolling-lobe flexible member. In the case of flexible members with conical sealing surfaces, the bead core ensures a secure fit and a permanent preload on the cone. The other end of the rolling-lobe flexible member has a fastening bead capable of being flanged. The edge of the terminating flange plate is flanged seal tight around the fastening bead.
As a result of the use of plastic for the bead cores, the expansion problem arising owing to the steel wires as reinforcement cores is duly avoided, but the load capacity of the plastic cores produced by injection molding is limited.